- Intermittent Malfunctions

NOTE: When a problem is intermittent the "Service Engine Soon" or "Check Engine" light may or may not be illuminated and a code will not necessarily stored.

NOTE: Do not use Trouble Code Charts to Diagnose intermittent problems. Use of these charts may result in the replacement of good parts.

CONDITION I
NOTE: In most cases, the cause of an intermittent problem can be traced to faulty electrical connectors or wiring. Diagnostics must include a careful inspection of the indicated circuit wiring and connectors as follows:

1. Terminals not fully seated in connector or poor mating of connector halves.
2. Improperly formed or damaged terminals. Carefully reform all connectors in problem circuit to increase contact tension.
3. HEI distributor EST wires must be routed away from distributor, ignition coil, secondary wiring and alternator.
4. Check circuits 419 and 451 for a short to ground.
5. Check ECM ground at engine block attachment, circuits 450 and 450R.
6. Electrical system interferences caused by a defective relay, ECM driven solenoid or a switch causing a sharp electrical surge. The problem will normally occur when the defective component is operated.
7. Improper installation of electrical options.
8. Open A/C clutch diode.

If a visual inspection does not reveal the cause of the problem proceed as follows:

1. Connect a voltmeter or Scan tool to the affected circuit.
2. While driving the vehicle have an assistant observe the meter or scan tool for any irregular voltage readings indicating a circuit problem.
3. If further inspection of the affected circuit reveals the connectors and wiring are good, and a Trouble Code (except Codes 44 and 45) was stored for a sensor circuit, substitute the affected sensor with a known good sensor then recheck that circuit.




CONDITION II
To Check for a loss of trouble code memory ground the dwell lead for at least 10 seconds with the "test" lead left ungrounded. A code 23 should be stored after the engine is stopped and the ignition is turned to "run". If this is not achieved the ECM is faulty.

CONDITION III
An intermittent "Service Engine Soon" light with no Trouble Code set may be caused by a sharp electrical surge in a faulty relay, ECM driven solenoid, or switch. This will most likely occur when the component is operational. To diagnose this condition, inspect the following
1. Proper installation of all optional electrical equipment.
2. Ensure EST wires are routed away from the alternator, ignition components and wires, and spark plug wires. Ensure the ECM ignition system wire has a good ground.
3. Check that the secondary ignition circuit is not shorted to ground.
4. Check the "Service Engine Soon" and "Diagnostic Test" leads for an intermittent short to ground.
5. Check all ECM grounds.